System and method for assigning control of a logical unit number

ABSTRACT

A method, computer program product, and computing system for receiving a first write request from a first host concerning a logical unit number (“LUN”). Exclusive control of the LUN is assigned to the first host. A write operation is performed on the LUN in response to the first write request. A second write request is received from a second host concerning the LUN. A second portion of the LUN that was exclusively controlled by the first host is reassigned so that the second portion of the LUN is exclusively controlled by the second host.

TECHNICAL FIELD

This disclosure relates to cache memory systems and, more particularly, to systems and methods for improving the performance of cache memory systems.

BACKGROUND

Storing and safeguarding electronic content is of paramount importance in modern business. Accordingly, various systems may be employed to protect such electronic content.

The use of solid-state storage devices is increasing in popularity. A solid state storage device is a content storage device that uses solid-state memory to store persistent content. A solid-state storage device may emulate (and therefore replace) a conventional hard disk drive. Additionally/alternatively, a solid state storage device may be used within a cache memory system. With no moving parts, a solid-state storage device largely eliminates (or greatly reduces) seek time, latency and other electromechanical delays and failures associated with a conventional hard disk drive.

SUMMARY OF DISCLOSURE

A computer-implemented method includes receiving a first write request from a first host concerning a LUN. Exclusive control of the LUN is assigned to the first host. A write operation is performed on the LUN in response to the first write request. A second write request is received from a second host concerning the LUN. A second portion of the LUN that was exclusively controlled by the first host is reassigned so that the second portion of the LUN is exclusively controlled by the second host.

One or more of the following features may be included. A write operation may be performed on the second portion of the LUN in response to the second write request. A third write request may be received from a third host concerning the LUN. A third portion of the LUN that was exclusively controlled by the first host may be reassigned so that the third portion of the LUN is exclusively controlled by the third host. A write operation may be performed on the third portion of the LUN in response to the third write request. A read request may be received from the second host concerning the LUN. A fourth portion of the LUN that was exclusively controlled by the first host may be reassigned so that the fourth portion of the LUN is jointly controlled by the first host and the second host. A read operation may be performed on the fourth portion of the LUN in response to the read request.

Assigning exclusive control of the LUN to the first host may include assigning exclusive control of the LUN in its entirety to the first host. The LUN may be included within a data array. One or more of the first host and the second host may be application servers.

In another implementation, a computer program product resides on a computer readable medium that has a plurality of instructions stored on it. When executed by a processor, the instructions cause the processor to perform operations including receiving a first write request from a first host concerning a LUN. Exclusive control of the LUN is assigned to the first host. A write operation is performed on the LUN in response to the first write request. A second write request is received from a second host concerning the LUN. A second portion of the LUN that was exclusively controlled by the first host is reassigned so that the second portion of the LUN is exclusively controlled by the second host.

One or more of the following features may be included. A write operation may be performed on the second portion of the LUN in response to the second write request. A third write request may be received from a third host concerning the LUN. A third portion of the LUN that was exclusively controlled by the first host may be reassigned so that the third portion of the LUN is exclusively controlled by the third host. A write operation may be performed on the third portion of the LUN in response to the third write request. A read request may be received from the second host concerning the LUN. A fourth portion of the LUN that was exclusively controlled by the first host may be reassigned so that the fourth portion of the LUN is jointly controlled by the first host and the second host. A read operation may be performed on the fourth portion of the LUN in response to the read request.

Assigning exclusive control of the LUN to the first host may include assigning exclusive control of the LUN in its entirety to the first host. The LUN may be included within a data array. One or more of the first host and the second host may be application servers.

In another implementation, a computing system includes at least one processor and at least one memory architecture coupled with the at least one processor, wherein the computing system is configured to perform operations including receiving a first write request from a first host concerning a LUN. Exclusive control of the LUN is assigned to the first host. A write operation is performed on the LUN in response to the first write request. A second write request is received from a second host concerning the LUN. A second portion of the LUN that was exclusively controlled by the first host is reassigned so that the second portion of the LUN is exclusively controlled by the second host.

One or more of the following features may be included. A write operation may be performed on the second portion of the LUN in response to the second write request. A third write request may be received from a third host concerning the LUN. A third portion of the LUN that was exclusively controlled by the first host may be reassigned so that the third portion of the LUN is exclusively controlled by the third host. A write operation may be performed on the third portion of the LUN in response to the third write request. A read request may be received from the second host concerning the LUN. A fourth portion of the LUN that was exclusively controlled by the first host may be reassigned so that the fourth portion of the LUN is jointly controlled by the first host and the second host. A read operation may be performed on the fourth portion of the LUN in response to the read request.

Assigning exclusive control of the LUN to the first host may include assigning exclusive control of the LUN in its entirety to the first host. The LUN may be included within a data array. One or more of the first host and the second host may be application servers.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a storage system and a data caching process coupled to a distributed computing network;

FIG. 2 is a diagrammatic view of the storage system of FIG. 1;

FIG. 3 is a diagrammatic view of a data write request for use with the data caching process of FIG. 1;

FIG. 4 is a diagrammatic view of a data read request for use with the data caching process of FIG. 1;

FIG. 5 is a diagrammatic view of a content directory for use with the data caching process of FIG. 1;

FIG. 6 is a first flow chart of the data caching process of FIG. 1;

FIGS. 7A-7D are detail views of a LUN included within the storage system of FIG. 2;

FIG. 8 is a second flow chart of the data caching process of FIG. 1;

FIG. 9A-9B are detail views of an ownership tracking structure for use by the data caching process of FIG. 1;

FIG. 10 is a detail view of a LUN included within the storage system of FIG. 2; and

FIG. 11 is a third flow chart of the data caching process of FIG. 1.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

General Information:

As will be appreciated by one skilled in the art, the present disclosure may be embodied as a method, system, or computer program product. Accordingly, the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, the present disclosure may take the form of a computer program product on a computer-usable storage medium having computer-usable program code embodied in the medium.

Any suitable computer usable or computer readable medium may be utilized. The computer-usable or computer-readable medium may be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a transmission media such as those supporting the Internet or an intranet, or a magnetic storage device. Note that the computer-usable or computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via, for instance, optical scanning of the paper or other medium, then compiled, interpreted, or otherwise processed in a suitable manner, if necessary, and then stored in a computer memory. In the context of this document, a computer-usable or computer-readable medium may be any medium that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer-usable medium may include a propagated data signal with the computer-usable program code embodied therewith, either in baseband or as part of a carrier wave. The computer usable program code may be transmitted using any appropriate medium, including but not limited to the Internet, wireline, optical fiber cable, RF, etc.

Computer program code for carrying out operations of the present disclosure may be written in an object oriented programming language such as Java, Smalltalk, C++ or the like. However, the computer program code for carrying out operations of the present disclosure may also be written in conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

The present disclosure is described below with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks.

The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

System Overview:

Referring to FIG. 1, there is shown data caching process 10 that may reside on and may be executed by storage system 12, which may be connected to network 14 (e.g., the Internet or a local area network). Examples of storage system 12 may include, but are not limited to: a Network Attached Storage (NAS) system, a Storage Area Network (SAN), one or more personal computers with a memory system, one or more server computers with a memory system, and a cloud-based device with a memory system.

As is known in the art, a SAN may include one or more of a personal computer, a server computer, a series of server computers, a mini computer, a mainframe computer, a RAID device and a NAS system. The various components of storage system 12 may execute one or more operating systems, examples of which may include but are not limited to: Microsoft Windows XP Server™; Novell Netware™; Redhat Linux™, Unix, or a custom operating system, for example.

The instruction sets and subroutines of data caching process 10, which may be stored on storage device 16 included within storage system 12, may be executed by one or more processors (not shown) and one or more memory architectures (not shown) included within storage system 12. Storage device 16 may include but is not limited to: a hard disk drive; a tape drive; an optical drive; a RAID device; a random access memory (RAM); a read-only memory (ROM); and all forms of flash memory storage devices.

Network 14 may be connected to one or more secondary networks (e.g., network 18), examples of which may include but are not limited to: a local area network; a wide area network; or an intranet, for example.

Various data requests (e.g. data request 20) may be sent from client applications 22, 24, 26, 28 to storage system 12. Examples of data request 20 may include but are not limited to data write requests (i.e. a request that content be written to storage system 12) and data read requests (i.e. a request that content be read from storage system 12).

The instruction sets and subroutines of client applications 22, 24, 26, 28, which may be stored on storage devices 30, 32, 34, 36 (respectively) coupled to client electronic devices 38, 40, 42, 44 (respectively), may be executed by one or more processors (not shown) and one or more memory architectures (not shown) incorporated into client electronic devices 38, 40, 42, 44 (respectively). Storage devices 30, 32, 34, 36 may include but are not limited to: hard disk drives; tape drives; optical drives; RAID devices; random access memories (RAM); read-only memories (ROM), and all forms of flash memory storage devices. Examples of client electronic devices 38, 40, 42, 44 may include, but are not limited to, personal computer 38, laptop computer 40, personal digital assistant 42, notebook computer 44, a server (not shown), a data-enabled, cellular telephone (not shown), and a dedicated network device (not shown).

Client electronic devices 38, 40, 42, 44 may each execute an operating system, examples of which may include but are not limited to Microsoft Windows™, Microsoft Windows CE™, Redhat Linux™, or a custom operating system.

Users 46, 48, 50, 52 may access storage system 12 directly through network 14 or through secondary network 18. Further, storage system 12 may be connected to network 14 through secondary network 18, as illustrated with link line 54.

The various client electronic devices may be directly or indirectly coupled to network 14 (or network 18). For example, personal computer 38 is shown directly coupled to network 14 via a hardwired network connection. Further, notebook computer 44 is shown directly coupled to network 18 via a hardwired network connection. Laptop computer 40 is shown wirelessly coupled to network 14 via wireless communication channel 56 established between laptop computer 40 and wireless access point (i.e., WAP) 58, which is shown directly coupled to network 14. WAP 58 may be, for example, an IEEE 802.11a, 802.11b, 802.11g, 802.11n, Wi-Fi, and/or Bluetooth device that is capable of establishing wireless communication channel 56 between laptop computer 40 and WAP 58. Personal digital assistant 42 is shown wirelessly coupled to network 14 via wireless communication channel 60 established between personal digital assistant 42 and cellular network/bridge 62, which is shown directly coupled to network 14.

As is known in the art, all of the IEEE 802.11x specifications may use Ethernet protocol and carrier sense multiple access with collision avoidance (i.e., CSMA/CA) for path sharing. The various 802.11x specifications may use phase-shift keying (i.e., PSK) modulation or complementary code keying (i.e., CCK) modulation, for example. As is known in the art, Bluetooth is a telecommunications industry specification that allows e.g., mobile phones, computers, and personal digital assistants to be interconnected using a short-range wireless connection.

The Data Caching Process:

For the following discussion, client application 22 is going to be described for illustrative purposes. However, this is not intended to be a limitation of this disclosure, as other client applications (e.g., client applications 24, 26, 28) may be equally utilized.

For illustrative purposes, storage system 12 will be described as being a network-based storage system that includes a plurality of electro-mechanical backend storage devices. However, this is for illustrative purposes only and is not intended to be a limitation of this disclosure, as other configurations are possible and are considered to be within the scope of this disclosure. For example and as discussed above, storage system 12 may be a personal computer that includes a single electro-mechanical storage device.

Referring also to FIG. 2, storage system 12 may include a server computer/controller (e.g. server computer/controller 100), and a plurality of storage targets T_(1-n) (e.g. storage targets 102, 104, 106, 108). Storage targets 102, 104, 106, 108 may be configured to provide various levels of performance and/or high availability. For example, one or more of storage targets 102, 104, 106, 108 may be configured as a RAID 0 array, in which data is striped across storage targets. By striping data across a plurality of storage targets, improved performance may be realized. However, RAID 0 arrays do not provide a level of high availability. Accordingly, one or more of storage targets 102, 104, 106, 108 may be configured as a RAID 1 array, in which data is mirrored between storage targets. By mirroring data between storage targets, a level of high availability is achieved as multiple copies of the data are stored within storage system 12.

While storage targets 102, 104, 106, 108 are discussed above as being configured in a RAID 0 or RAID 1 array, this is for illustrative purposes only and is not intended to be a limitation of this disclosure, as other configurations are possible. For example, storage targets 102, 104, 106, 108 may be configured as a RAID 3, RAID 4, RAID 5 or RAID 6 array.

While in this particular example, storage system 12 is shown to include four storage targets (e.g. storage targets 102, 104, 106, 108), this is for illustrative purposes only and is not intended to be a limitation of this disclosure. Specifically, the actual number of storage targets may be increased or decreased depending upon e.g. the level of redundancy/performance/capacity required.

Storage system 12 may also include one or more coded targets 110. As is known in the art, a coded target may be used to store coded data that may allow for the regeneration of data lost/corrupted on one or more of storage targets 102, 104, 106, 108. An example of such a coded target may include but is not limited to a hard disk drive that is used to store parity data within a RAID array.

While in this particular example, storage system 12 is shown to include one coded target (e.g., coded target 110), this is for illustrative purposes only and is not intended to be a limitation of this disclosure. Specifically, the actual number of coded targets may be increased or decreased depending upon e.g. the level of redundancy/performance/capacity required.

Examples of storage targets 102, 104, 106, 108 and coded target 110 may include one or more electro-mechanical hard disk drives, wherein a combination of storage targets 102, 104, 106, 108 and coded target 110 may form non-volatile, electro-mechanical memory system 112.

The manner in which storage system 12 is implemented may vary depending upon e.g. the level of redundancy/performance/capacity required. For example, storage system 12 may be a RAID device in which server computer/controller 100 is a RAID controller card and storage targets 102, 104, 106, 108 and/or coded target 110 are individual “hot-swappable” hard disk drives. An example of such a RAID device may include but is not limited to an NAS device. Alternatively, storage system 12 may be configured as a SAN, in which server computer/controller 100 may be e.g., a server computer and each of storage targets 102, 104, 106, 108 and/or coded target 110 may be a RAID device and/or computer-based hard disk drive. Further still, one or more of storage targets 102, 104, 106, 108 and/or coded target 110 may be a SAN.

In the event that storage system 12 is configured as a SAN, the various components of storage system 12 (e.g. server computer/controller 100, storage targets 102, 104, 106, 108, and coded target 110) may be coupled using network infrastructure 114, examples of which may include but are not limited to an Ethernet (e.g., Layer 2 or Layer 3) network, a fiber channel network, an InfiniBand network, or any other circuit switched/packet switched network.

Storage system 12 may execute all or a portion of data caching process 10. The instruction sets and subroutines of data caching process 10, which may be stored on a storage device (e.g., storage device 16) coupled to server computer/controller 100, may be executed by one or more processors (not shown) and one or more memory architectures (not shown) included within server computer/controller 100. Storage device 16 may include but is not limited to: a hard disk drive; a tape drive; an optical drive; a RAID device; a random access memory (RAM); a read-only memory (ROM); and all forms of flash memory storage devices.

As discussed above, various data requests (e.g. data request 20) may be generated. For example, these data requests may be sent from client applications 22, 24, 26, 28 to storage system 12. Additionally/alternatively and when server computer/controller 100 is configured as an application server, these data requests may be internally generated within server computer/controller 100. Examples of data request 20 may include but are not limited to data write request 116 (i.e. a request that content 118 be written to storage system 12) and data read request 120 (i.e. a request that content 118 be read from storage system 12).

Server computer/controller 100 may include input-output logic 122 (e.g., a network interface card or a Host Bus Adaptor (HBA)), processing logic 124, and first cache system 126. Examples of first cache system 126 may include but are not limited to a volatile, solid-state, cache memory system (e.g., a dynamic RAM cache memory system) and/or a non-volatile, solid-state, cache memory system (e.g., a flash-based, cache memory system).

During operation of server computer/controller 100, content 118 to be written to storage system 12 may be received by input-output logic 122 (e.g. from network 14 and/or network 18) and processed by processing logic 124. Additionally/alternatively and when server computer/controller 100 is configured as an application server, content 118 to be written to storage system 12 may be internally generated by server computer/controller 100. As will be discussed below in greater detail, processing logic 124 may initially store content 118 within first cache system 126.

Depending on the manner in which first cache system 126 is configured, processing logic 124 may immediately write content 118 to second cache system 128/non-volatile, electro-mechanical memory system 112 (if first cache system 126 is configured as a write-through cache) or may subsequently write content 118 to second cache system 128/non-volatile, electro-mechanical memory system 112 (if first cache system 126 is configured as a write-back cache). Additionally and in certain configurations, processing logic 124 may calculate and store coded data on coded target 110 (included within non-volatile, electro-mechanical memory system 112) that may allow for the regeneration of data lost/corrupted on one or more of storage targets 102, 104, 106, 108. For example, if processing logic 124 was included within a RAID controller card or a NAS/SAN controller, processing logic 124 may calculate and store coded data on coded target 110. However, if processing logic 124 was included within e.g., an application server, data array 130 may calculate and store coded data on coded target 110.

Examples of second cache system 128 may include but are not limited to a volatile, solid-state, cache memory system (e.g., a dynamic RAM cache memory system) and/or a non-volatile, solid-state, cache memory system (e.g., a flash-based, cache memory system).

The combination of second cache system 128 and non-volatile, electromechanical memory system 112 may form data array 130, wherein first cache system 126 may be sized so that the number of times that data array 130 is accessed may be reduced. Accordingly, by sizing first cache system 126 so that first cache system 126 retains a quantity of data sufficient to satisfy a significant quantity of data requests (e.g., data request 20), the overall performance of storage system 12 may be enhanced. As will be described below in greater detail, first cache system 126 may be a content-aware cache system.

Further, second cache system 128 within data array 130 may be sized so that the number of times that non-volatile, electromechanical memory system 112 is accessed may be reduced. Accordingly, by sizing second cache system 128 so that second cache system 128 retains a quantity of data sufficient to satisfy a significant quantity of data requests (e.g., data request 20), the overall performance of storage system 12 may be enhanced. As will be described below in greater detail, second cache system 128 may be a content-aware cache system.

As discussed above, the instruction sets and subroutines of data caching process 10, which may be stored on storage device 16 included within storage system 12, may be executed by one or more processors (not shown) and one or more memory architectures (not shown) included within storage system 12. Accordingly, in addition to being executed on server computer/controller 100, some or all of the instruction sets and subroutines of data caching process 10 may be executed by one or more processors (not shown) and one or more memory architectures (not shown) included within data array 130.

Referring also to FIGS. 3-4, data request 20 (e.g. data read request 116 and/or data write request 120) may be processed by server computer/controller 100 to extract pertinent information concerning these data requests.

When data request 20 is a data write request (e.g., write request 116), write request 116 may include content 118 to be written to data array 130. Additionally, write request 116 may include a storage address 200 that defines the intended storage location within storage array 130 at which content 118 is to be stored. For example, storage address 200 may define a particular logical unit within data array 130 (e.g., a LUN or Logical Unit Number) and a particular storage address within that specific logical unit (e.g., an LBA or Logical Block Address) for storing content 118.

Concerning read request 120, these requests do not include any content to be written to data array 130, as these are read requests and concern content to be read from data array 130. Read request 120 may include a storage address 202 that defines the storage location within storage array 130 from which content is to be retrieved. For example, storage address 202 may define a particular logical unit within data array 130 (e.g., a LUN or Logical Unit Number) and a particular storage address within that specific logical unit (e.g., an LBA or Logical Block Address) for retrieving the content sought from data array 130.

As will be discussed below in greater detail and referring also to FIG. 5, data caching process 10 may maintain content directory 250, which may be used to locate various pieces of content within first cache system 126. In one particular embodiment of content directory 250, content directory 250 may include plurality of entries 252, wherein each of these entries may identify: data array storage address 200/202 (e.g. a logical storage unit and a storage address at which a specific piece of previously-written content is located within storage array 130); first cache address 254 (e.g., the location within first cache system 126 at which the specific piece of previously-written content is also located), and content identifier 256 for the specific piece of previously-written content. Accordingly, content directory 250 may identify the location of specific pieces of content included within first cache system 126 and their corresponding pieces of data within data array 130, as well as a content identifier that uniquely identifies the specific piece of content.

Content identifier 256 may be used in a content-aware caching system and may, specifically, be a mathematical representation of the specific piece of previously-written content that may allow e.g. server computer/controller 100 to quickly determine whether two pieces of previously-written content are identical, as identical pieces of content would have identical content identifiers. In one particular embodiment, content identifier 256 may be a hash function (e.g., a cryptographic hash) of the previously-written content. Accordingly, through the use of a content-aware caching system, duplicate data entries within first cache system 126 and/or second cache system 128 may be quickly identified, avoided, and/or eliminated.

As is known in the art, a hash function is an algorithm/subroutine that maps large data sets to smaller data sets. The values returned by a hash function are typically called hash values, hash codes, hash sums, checksums or simply hashes. Hash functions are mostly used to accelerate table lookup or data comparison tasks such as e.g., finding items in a database and detecting duplicated or similar records in a large file.

General Read Request Processing:

During operation of server computer/controller 100, data caching process 10 may receive read request 120 on first cache system 126, wherein read request 120 identifies previously-written content (as defined by storage address 202) included within data array 130.

For example, assume that user 46 is using client application 22 to access data (i.e. content 132) that is currently being stored on data array 130. Accordingly, client application 22 may generate read request 120 which, as discussed above, may define a particular logical unit within data array 130 (e.g., a LUN or Logical Unit Number) and a particular storage address within that specific logical unit (e.g., an LBA or Logical Block Address) for retrieving content 132 sought from data array 130 by client application 22.

Assume that read request 120 defines LUN0/LBA5 as the location of content 132 within data array 130. Upon receiving read request 120, data caching process 10 may compare the location of content 132 within data array 130 (namely LUN0/LBA5) with each of the plurality of entries 252 defined within content directory 250 to determine if a copy of content 132 is locally available (i.e., cached) within first cache system 126. If LUN0/LBA5 was defined within content directory 250 (meaning that a local cached copy of content 132 is present/available within first cache system 126), that particular entry would also define a corresponding first cache address (e.g. first cache address 254) within first cache system 126 at which content 132 would be locally-available and retrievable from the first cache system 126. Conversely, in the event that LUN0/LBA5 is not defined within content directory 250 (meaning that a local cached copy of content 132 is not present/available within first cache system 126), data caching process 10 may need to obtain content 132 identified in read request 120 from data array 130.

In this particular example, since LUN0/LBA5 is not defined within content directory 250, a local cached copy of content 132 is not present/available within first cache system 126 and data caching process 10 will be need to obtain content 132 from data array 130.

Once content 132 is obtained by data caching process 10 from data array 130, data caching process 10 may store content 132 within first cache system 126 and may provide content 132 to client application 22, thus satisfying read request 120. Additionally, content directory 250 may be amended by data caching process 10 to include an entry (e.g., entry 258) that defines the data array storage address 200/202 (e.g. LUN0/LBA5); first cache address 254 (e.g., 111110), and content identifier 256 (e.g., ablccba) for content 132.

As discussed above, data array 130 may include second cache system 128. Accordingly, data caching process 10 may execute the above-described functionality with respect to second cache system 128.

General Write Request Processing:

During operation of server computer/controller 100, data caching process 10 may receive write request 116 on first cache system 126, wherein write request 116 identifies new content (e.g., content 118) to be written to data array 130.

For example, assume that user 46 is using client application 22 to create content (i.e. content 118) that is to be stored on data array 130. Accordingly, client application 22 may generate write request 116 which, as discussed above, may define a particular logical unit within data array 130 (e.g., a LUN or Logical Unit Number) and a particular storage address within that specific logical unit (e.g., an LBA or Logical Block Address) for storing content 118 within data array 130.

As discussed above and depending on the manner in which first cache system 126 is configured, data caching process 10 may immediately write content 118 to data array 130 (if first cache system 126 is configured as a write-through cache) or may subsequently write content 118 to data array 130 (if first cache system 126 is configured as a write-back cache).

Assuming that first cache system 126 in this example is configured as a write-through cache, data caching process 10 may immediately write content 118 to LUN0/LBA0 within data array 130 (as defined within write request 116). Additionally, data caching process 10 may locally-store content 118 within first cache system 126 and may amend content directory 250 to include an entry (e.g., entry 260) that defines the data array storage address 200/202 (e.g. LUN0/LBAO); first cache address 254 (e.g., 001011), and content identifier 256 (e.g., acdfcla) for content 118.

As discussed above, data array 130 may include second cache system 128. Accordingly, data caching process 10 may execute the above described functionality with respect to second cache system 128.

Content Aware Caching

As discussed above, content directory 250 may include a content identifier 256 that may be used in a content-aware caching system. A typical example of content identifier 256 may include but is not limited to a hash function of the content that content identifier 256 is associated with. Accordingly, through the use of content identifier 256 within a content-aware caching system, duplicate data entries within first cache system 126 and/or second cache system 128 may be quickly identified, avoided, and/or eliminated.

For example, upon receiving write request 116 and content 118, data caching process 10 may generate content identifier 256 for content 118. As discussed above, content identifier 256 generated for the content (i.e., content 118) identified within write request 116 may be a hash function (e.g., a cryptographic hash) of content 118.

Assume for illustrative purposes that write request 116 includes storage address 200 that defines the intended storage location for content 118 as LUN0/LBAO. Accordingly, upon receiving write request 116, data caching process 10 may generate content identifier 256 for content 118. Assume for illustrative purposes that data caching process 10 generates a hash of content 118, resulting in the generation of content identifier 256 (namely hash value acdfcla).

This newly-generated content identifier 256 (i.e. acdfcla) associated with content 118 may be compared to each of the other content identifiers (namely abalaby, alazchb, abalabz, alazcha) included within content directory 250 for first cache system 126 to determine if the newly-generated content identifier 256 (i.e. acdfcla) matches any of the other content identifiers (namely abalaby, alazchb, abalabz, alazcha) included within content directory 250.

As discussed above, each entry of the plurality of entries 252 included within content directory 250 is associated with a unique piece of content included within (in this example) first cache system 126. Accordingly, each unique content identifier included within content directory 250 may be associated with a unique piece of content written to (in this example) first cache system 126.

If, when performing this comparison, data caching process 10 does not identify a content identifier (i.e., abalaby, alazchb, abalabz, alazcha) within content directory 250 that matches the above-described, newly-generated content identifier (i.e. acdfcla), data caching process 10 may write content 118 to (in this example) first cache system 126 and may provide a copy of content 118 to data array 130 for storage within data array 130. Additionally, data caching process 10 may modify content directory 250 to include a new entry (i.e., entry 260) that defines the newly-generated content identifier (i.e. acdfcla), the location of content 118 within (in this example) first cache system 126 (i.e., 001011), and the location of content 118 within data array 130 (i.e., LUN0/LBAO).

If, when performing this comparison, data caching process 10 identified a content identifier within content directory 250 that matched the above-described, newly-generated content identifier (i.e. acdfcla), data caching process 10 would perform differently.

To illustrate how data caching process 10 would react if it found a matching content identifier, further assume for illustrative purposes that a second write request (i.e., write request 116′) includes storage address 200′ that defines the intended storage location for content 118′ as LUN0/LBA2. Accordingly, upon receiving write request 116′, data caching process 10 may generate content identifier 256 for content 118′. Assume for illustrative purposes that data caching process 10 generates a hash of content 118′, resulting in the generation of content identifier 256 (namely hash value alazcha).

This newly-generated content identifier 256 (i.e. alazcha) associated with content 118′ may be compared to each of the other content identifiers (namely abalaby, alazchb, abalabz, alazcha) included within content directory 250 for (in this example) first cache system 126 to determine if the newly-generated content identifier 256 (i.e. alazcha) matches any of the other content identifiers (namely abalaby, alazchb, abalabz, alazcha) included within content directory 250.

If, when performing this comparison, data caching process 10 does identify a content identifier (namely alazcha) within content directory 250 that matches the above-described, newly-generated content identifier (i.e. alazcha), data caching process 10 may perform a couple of functions.

For example, data caching process 10 may modify the entry (i.e., entry 262) within content directory 250 that is associated with the matching content identifier (i.e., alazcha) to include storage address 200′ that defines the intended storage location for content 118′ (i.e., LUN0/LBA2 within data array 130), thus generating modified entry 262′. Accordingly, modified entry 262′ identifies that the pieces of content that are currently stored at LUN4/LBA7 and LUN0/LBA2 within data array 130 are identical. Accordingly, a single piece of cached content (located at first cache address 010111 within, in this example, first cache system 126) may be used as a local cached copy for both pieces of content stored on data array 130.

While the system is described above as modifying entry 262 by adding a second LUN/LBA designation to generate modified entry 262′, this is for illustrative purposes only and is not intended to be a limitation of this disclosure, as other configurations are possible. For example, sub-tables/sub-entries may be utilized to show the manner in which multiple LUNs/LBAs are mapped to a single piece of content within, for example, first cache system 126.

As discussed above, data array 130 may include second cache system 128. Accordingly, data caching process 10 may execute the above-described content aware functionality with respect to second cache system 128.

Managing Access to LUNs

Assume for illustrative purposes that a second server computer/controller (e.g. server computer/controller 134) is also coupled to data array 130 via network infrastructure 114. Accordingly, each of server computer/controller 100 and server computer/controller 134 may gain control and relinquish control of the various logical units (e.g. LUNs) within data array 130. Further, each of server computer/controller 100 and server computer/controller 134 may write data to and read data from various storage addresses (e.g., an LBA or Logical Block Address) within the LUNs included in data array 130.

Accordingly, problems may be realized when e.g. server computer/controller 100 and server computer/controller 134 perform tasks that are in conflict with each other. For illustrative purposes, assume that a first server computer/controller (e.g. server computer/controller 100) writes a piece of content (e.g. content 118) to an address (e.g. LUN0/LBA2) within storage array 130. As discussed above, a copy of this content (e.g. content 118) will also be written to first cache system 126. Further assume that a second server computer/controller (e.g. server computer/controller 134) writes a piece of content (e.g. content 136) to the same address (e.g. LUN0/LBA2) within storage array 130. Similarly, a copy of this content (e.g. content 136) would also be written to a local cache system (e.g., cache system 138) within server computer/controller 134.

Accordingly and in this situation, if a read request is received concerning LUN0/LBA2 within data array 130, the data provided to the requester will vary depending upon which server computer/controller fulfills the request. For example, if the read request was received by server computer/controller 134, server computer/controller 134 would fulfill the read request by providing the locally-cached copy of the data (which is stored within cache system 138 of server computer/controller 134). In this situation, the data provided to the requester would be correct, in that the cached data matches the data stored at LUN0/LBA2 within data array 130.

However, if the read request was received by server computer/controller 100, server computer/controller 100 would also fulfill the read request by providing the locally-cached copy of the data (which is stored within first cache system 126 of server computer/controller 100). Unfortunately and in this situation, the data provided to the requester would be incorrect, in that the cached data does not match the data stored at LUN0/LBA2 within data array 130.

In order to avoid such a situation in which multiple hosts believe that they simultaneously control a single LUN, data caching process 10 may only assign control of individual LUNs on an “as needed” basis.

Referring also to FIG. 6 & FIGS. 7A-7D, assume that the individual LUNs included within data array 130 are initially not assigned to any specific host. For example and as discussed above, assume that LUN 0 at the time of system startup is not assigned to any host. LUN 0 may continue to be unassigned until a host expresses interest in LUN 0. Accordingly, assume that data caching process 10 receives 300 first write request 350 from a first host (e.g., server computer/controller 100) concerning LUN 0. In response to receiving 300 first write request 350, data caching process 10 may initially assign 302 exclusive control of all of LUN 0 to the first host (e.g., server computer/controller 100). Accordingly, the entirety of LUN 0 may be assigned 302 to the first host (e.g., server computer/controller 100) and, therefore, LUN 0 is not being shared with any other host at this point in time. In this particular example, LUN 0 is shown to include eight illustrative portions. Therefore, data caching process 10 may assign all eight portions of LUN 0 to server computer/controller 100 in response to first write request 350.

While the system is described above as assigning excusive access to a LUN in response to receipt of a first write request, this is for illustrative purposes only and is not intended to be a limitation of this disclosure, as other configurations are possible. For example, the above-described system may assign exclusive access to a LUN in response to receipt of a first read request.

Further assume for illustrative purposes that data caching process 10 may perform 304 a write operation on LUN 0 in response to first write request 350. Accordingly, any content provided with respect to first write request 350 may be written to LUN 0.

Additionally, assume for illustrative purposes that data caching process 10 receives 306 second write request 352 from a second host (e.g., server computer/controller 134) concerning LUN 0. As discussed above, in response to data caching process 10 receiving 300 first write request 350, data caching process 10 initially assigned 302 exclusive control of all of LUN 0 to the first host (e.g., server computer/controller 100).

However, in response to the data caching process 10 receiving 306 second write request 352, data caching process 10 may reassign 308 second portion 354 of LUN 0 that was initially exclusively controlled by the first host (e.g., server computer/controller 100) so that second portion 354 of LUN 0 is exclusively controlled by the second host (e.g., server computer/controller 134). Data caching process 10 may perform 310 a write operation on second portion 354 of LUN 0 in response to second write request 352. Accordingly, any content provided with respect to second write request 352 may be written to second portion 354 of LUN 0. The size of second portion 354 of LUN 0 may be configured to accommodate the data that is being written to LUN 0 in accordance with second write request 352.

Further, assume for illustrative purposes that data caching process 10 receives 312 third write request 356 from a third host (not shown) concerning LUN 0. As discussed above, in response to data caching process 10 receiving 300 first write request 350, data caching process 10 initially assigned 302 exclusive control of all of LUN 0 to the first host (e.g., server computer/controller 100) and subsequently reassigned 308 second portion 354 of LUN 0 to second host (e.g., server computer/controller 134).

However, in response to the data caching process 10 receiving 312 third write request 356, data caching process 10 may reassign 314 third portion 358 of LUN 0 that was initially exclusively controlled by the first host (e.g., server computer/controller 100) so that third portion 358 of LUN 0 is exclusively controlled by the third host (not shown). Data caching process 10 may perform 316 a write operation on third portion 358 of LUN 0 in response to third write request 356. Accordingly, any content provided with respect to third write request 356 may be written to third portion 358 of LUN 0. The size of third portion 358 of LUN 0 may be configured to accommodate the data that is being written to LUN 0 in accordance with third write request 356.

Further, assume for illustrative purposes that data caching process 10 receives 318 read request 360 from a second host (e.g., server computer/controller 134) concerning LUN 0. As discussed above, in response to data caching process 10 receiving 300 first write request 350, data caching process 10 initially assigned 302 exclusive control of all of LUN 0 to the first host (e.g., server computer/controller 100), subsequently reassigned 308 second portion 354 of LUN 0 to second host (e.g., server computer/controller 134), and subsequently reassigned 314 third second portion 358 of LUN 0 to a third host (not shown)

However, in response to the data caching process 10 receiving 318 read request 360, data caching process 10 may reassign 320 fourth portion 362 of LUN 0 that was initially exclusively controlled by the first host (e.g., server computer/controller 100) so that fourth portion 362 of LUN 0 is jointly controlled by the first host (e.g., server computer/controller 100) and the second host (e.g., server computer/controller 134). In this particular situation, joint control of fourth portion 362 is possible, as the request received by data caching process 10 was read request 360. Had the request received been a write request, fourth portion 362 of LUN 0 would have been exclusively controlled by the host making the request.

Data caching process 10 may perform 322 a read operation on fourth portion 362 of LUN 0 in response to read request 360. Accordingly, any content requested with respect to read request 360 may be retrieved from fourth portion 362 of LUN 0. The size of fourth portion 362 of LUN 0 may be configured to accommodate the data that is being read from LUN 0 in accordance with read request 360.

While the system is described above as read request 360 being the fourth request received (after three write requests), this is for illustrative purposes only and is not intended to be a limitation of this disclosure, as other configurations are possible. For example, if read request 360 was the second request received, the above-described system would process it in the same manner.

Referring also to FIGS. 8, 9A & 9B and as discussed above, in accordance with various write requests and read request received by data caching process 10, data caching process 10 that may compartmentalize 400 e.g., LUN 0 into a plurality of portions (e.g., portions 354, 358, 362) that are each assigned to one or more hosts (e.g., server computer/controller 100 and/or server computer/controller 134).

In order to keep track of all these various portions, data caching process 10 may maintain 402 ownership tracking structure 450 for LUN 0. Ownership tracking structure 450 may include a data entry (e.g., data entries for 452, 454, 456, 458, 460, 462) associated with each of the plurality of portions (labeled portions 1-6) within LUN 0. As illustrated in FIG. 9:

-   -   Data entry 452 identifies data portion #1, which begins at         location 0 within LUN 0, ends at location 2 within LUN 0, and is         exclusively controlled by Host 1;     -   Data entry 454 identifies data portion #2, which begins at         location 2 within LUN 0, ends at location 3 within LUN 0, and is         exclusively controlled by Host 2;     -   Data entry 456 identifies data portion #3, which begins at         location 3 within LUN 0, ends at location 5 within LUN 0, and is         exclusively controlled by Host 1;     -   Data entry 458 identifies data portion #4, which begins at         location 5 within LUN 0, ends at location 6 within LUN 0, and is         exclusively controlled by Host 3;     -   Data entry 460 identifies data portion #5, which begins at         location 6 within LUN 0, ends at location 7 within LUN 0, and is         exclusively controlled by Host 1; and     -   Data entry 362 identifies data portion #6, which begins at         location 7 within LUN 0, ends at location 8 within LUN 0, and is         jointly controlled by Hosts 1&2.

As is illustrated above and in FIG. 9A, as the number of portions within a LUN increases, the size of ownership tracking structure 450 increases proportionally. For example, assume for illustrative purposes that each data entry within ownership tracking structure 450 consumes 10 kB of storage space. Accordingly, when LUN 0 is initially assigned in its entirety, LUN 0 is “divided” into a single portion. Accordingly, ownership tracking structure 450 would be 10 kB in size. However, if e.g. LUN 0 was divided into 1,200 portions, ownership tracking structure 450 would balloon to 12 MB in size. Accordingly, data caching process 10 may monitor 404 one or more properties of ownership tracking structure 450 to determine if ownership tracking structure 450 should be compressed.

When monitoring 404 the properties of ownership tracking structure 450, data caching process 10 may e.g. monitor 406 the total size of ownership tracking structure 450 and/or monitor 408 the quantity of data entries included within ownership tracking structure 450, as both of these values are indicative of the overall size of ownership tracking structure 450.

For example, data caching process 10 may e.g. define a maximum quantity of data entries for ownership tracking structure 450, wherein when that amount is exceeded, data caching process 10 may take steps to compress ownership tracking structure 450. Alternatively, data caching process 10 may e.g. define a maximum file size for ownership tracking structure 450, wherein when that file size is exceeded, data caching process 10 may take steps to compress ownership tracking structure 450.

In the event that data caching process 10 determines that ownership tracking structure 450 needs to be compressed, data caching process 10 may take 410 one or more actions to reduce the size of ownership tracking structure 450. When taking 410 one or more actions to reduce the size of ownership tracking structure 450, data caching process 10 may identify 412 one or more combinable portions within LUN 0 that may be combined with one or more other portions within LUN 0 to make a smaller quantity of larger portions within LUN 0. When identifying 412 combinable portions, data caching process 10 may identify 414 lesser-used portions within LUN 0.

In order to determine which portions within LUN 0 are lesser-used portions, data caching process 10 may review a Least Recently Used (LRU) list that may be configured to identify the portions of LUN 0 (or data extents/data items within LUN 0) that were used the least, wherein the deletion of lesser-used portions of LUN 0 has less of an adverse impact on the performance of the above-describe system then the deletion of highly-used portions of LUN 0. Once the one or more combinable portions within LUN 0 are identified 412 by data caching process 10, data caching process 10 may combine 416 these combinable portions with other portions within LUN 0 to form a larger portion within LUN 0.

Referring again to FIG. 7D, assume that second portion 354 of LUN 0 that was exclusively controlled by the second host (e.g., server computer/controller 134) is rarely used and deemed to be a combinable portion by data caching process 10. Accordingly, second portion 354 of LUN 0 may be deleted by data caching process 10 and combined 416 with portions 364, 366 of LUN 0, which are both exclusively controlled by the first host (e.g., server computer/controller 100). Accordingly, second portion 354 of LUN 0 may be combined 416 by data caching process 10 with portions 364, 366 of LUN 0 to form a larger portion (e.g. consolidated portion 500, FIG. 10) within LUN 0.

In response to combining 416 portions 354, 364 and 366 of LUN 0, data caching process 10 update 418 ownership tracking structure 450 to remove the data entries associated with the one or more combinable portions (e.g. deleted portion 354), resulting in data caching process 10 generating modified ownership tracking structure 450′, which only includes four entries (namely data entries 452, 458, 460, 462), wherein data entry 452 defines consolidated portion 500 within LUN 0 that begins at location 0 within LUN 0 and ends at location 5 within LUN 0.

Additionally, data caching process 10 may notify 420 the various hosts (namely server computer/controller 134) that were associated with the combinable portions (namely portion 354) that portion 354 is being deleted. Such a notification issued by data caching process 10 may include a cache invalidate request that provides instructions to e.g., server computer/controller 134 to invalidate any and all cash entries (e.g. within the cache system 138) that contain locally-cached data that corresponds to data that was written to and stored within portion 354 of LUN 0, which is now under the control of server computer/controller 100.

Referring also to FIG. and as discussed above, in accordance with various write requests and read request received by data caching process 10, data caching process 10 that may compartmentalize 400 e.g., LUN 0 into a plurality of portions (e.g., portions 354, 358, 362) that are each assigned to one or more hosts (e.g., server computer/controller 100 and/or server computer/controller 134).

As also discussed above, in order to keep track of all these various portions, data caching process 10 may maintain 402 ownership tracking structure 450 (see FIG. 9A) for LUN 0. Ownership tracking structure 450 (see FIG. 9A) may include a data entry (e.g., data entries for 452, 454, 456, 458, 460, 462) associated with each of the plurality of portions (labeled portions 1-6) within LUN 0.

As discussed above, one or more of the first host (e.g., server computer/controller 100) and the second host (e.g., server computer/controller 134) may be application servers. As is known in the art and for various reasons, applications that are running on one host may sometimes be migrated (i.e. moved) to another host. For example, if server computer/controller 100 (i.e., host 1) is currently running a database application and server computer/controller 100 is going to be shut down for maintenance, the database application may be migrated to e.g. server computer/controller 134 (i.e., host 2).

Data caching process 10 may monitor for the occurrence of such migration events with respect to e.g. LUN 0. In the event that data caching process 10 detects 550 the occurrence of such a migration event (wherein an application that is being executed on a first host is being migrated so that the application can be executed on a second host), data caching process 10 may identify 552 any portions within e.g. LUN 0 that are assigned to the application currently being executed on the first host, thus generating one or more identified portions.

Continuing with the above-stated example and for illustrative purposes, assume that database application 140 (see FIG. 2) is currently being executed on server computer/controller 100. However, server computer/controller 100 has too high of a utilization rate and needs to be load balanced. Further, assume that as database application 140 is of critical importance, database application 140 must be migrated to another host (as opposed to being shut down and restarted). Accordingly, a migration event might take place in which database application 140 is migrated from server computer/controller 100 to server computer/controller 134. Accordingly, data caching process 10 would detect 550 the occurrence of this migration event.

As database application 140 is running on server computer/controller 100 and portion 502 (see FIG. 10) of LUN 0 is assigned to and control by server computer/controller 100, assume for illustrative purposes that data caching process 10 identifies 552 portion 502 within LUN 0 as being assigned to database application 140, thus generating one identified portion.

Accordingly, data caching process 10 may reassign 554 this identified portion (namely portion 502) from server computer/controller 100 (i.e. host 1) to server computer/controller 134 (i.e. host 2). Data caching process 10 may notify 556 server computer/controller 100 (i.e. host 1) that the identified portion (namely portion 502) is being reassigned 554 to server computer/controller 134 (i.e. host 2).

When notifying 556 server computer/controller 100, data caching process 10 may provide 558 server computer/controller 100 with one or more cache invalidate requests. These cache invalidate request may provide instructions to e.g., server computer/controller 100 to invalidate any and all cache entries (e.g. within the cache system 100) that contain locally-cached data that corresponds to data that was written to and stored within portion 502 of LUN 0, which is now under the control of server computer/controller 134.

In response to reassigning 554 portion 502 from server computer/controller 100 to server computer/controller 134, data caching process 10 update 560 ownership tracking structure 450 to reflect reassignment 554 of portion 502 from server computer/controller 100 to server computer/controller 134. Accordingly, data entry 460 within ownership tracking structure 450 may be updated to show the above-described reassignment 554.

As will be appreciated by one skilled in the art, the present disclosure may be embodied as a method, system, or computer program product. Accordingly, the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, the present disclosure may take the form of a computer program product on a computer-usable storage medium having computer-usable program code embodied in the medium.

The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.

A number of implementations have been described. Having thus described the disclosure of the present application in detail and by reference to embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the disclosure defined in the appended claims. 

What is claimed is:
 1. A computer-implemented method comprising: receiving, by a processor, a first write request from a first host concerning a logical unit number (“LUN”); assigning, by the processor, exclusive control of the LUN to the first host; performing, by the processor, a write operation on the LUN in response to the first write request; receiving, by the processor, a second write request from a second host concerning the LUN; and reassigning, by the processor, a second portion of the LUN that was exclusively controlled by the first host so that the second portion of the LUN is exclusively controlled by the second host.
 2. The computer-implemented method of claim 1 further comprising: performing, by the processor, a write operation on the second portion of the LUN in response to the second write request.
 3. The computer-implemented method of claim 1 further comprising: receiving, by the processor, a third write request from a third host concerning the LUN; reassigning, by the processor, a third portion of the LUN that was exclusively controlled by the first host so that the third portion of the LUN is exclusively controlled by the third host; and performing, by the processor, a write operation on the third portion of the LUN in response to the third write request.
 4. The computer-implemented method of claim 1 further comprising: receiving, by the processor, a read request from the second host concerning the LUN; reassigning, by the processor, a fourth portion of the LUN that was exclusively controlled by the first host so that the fourth portion of the LUN is jointly controlled by the first host and the second host; and performing, by the processor, a read operation on the fourth portion of the LUN in response to the read request.
 5. The computer-implemented method of claim 1 wherein assigning exclusive control of the LUN to the first host includes: assigning, by the processor, exclusive control of the LUN in its entirety to the first host.
 6. The computer-implemented method of claim 1 wherein the LUN is included within a data array.
 7. The computer-implemented method of claim 1 wherein one or more of the first host and the second host are application servers.
 8. A computer program product residing on a non-transitory computer readable medium having a plurality of instructions stored thereon which, when executed by a processor, cause the processor to perform operations comprising: receiving a first write request from a first host concerning a logical unit number (“LUN”); assigning exclusive control of the LUN to the first host; performing a write operation on the LUN in response to the first write request; receiving a second write request from a second host concerning the LUN; and reassigning a second portion of the LUN that was exclusively controlled by the first host so that the second portion of the LUN is exclusively controlled by the second host.
 9. The computer program product of claim 8 further comprising instructions for: performing a write operation on the second portion of the LUN in response to the second write request.
 10. The computer program product of claim 8 further comprising instructions for: receiving a third write request from a third host concerning the LUN; reassigning a third portion of the LUN that was exclusively controlled by the first host so that the third portion of the LUN is exclusively controlled by the third host; and performing a write operation on the third portion of the LUN in response to the third write request.
 11. The computer program product of claim 8 further comprising instructions for: receiving a read request from the second host concerning the LUN; reassigning a fourth portion of the LUN that was exclusively controlled by the first host so that the fourth portion of the LUN is jointly controlled by the first host and the second host; and performing a read operation on the fourth portion of the LUN in response to the read request.
 12. The computer program product of claim 8 wherein the instructions for assigning exclusive control of the LUN to the first host include instructions for: assigning exclusive control of the LUN in its entirety to the first host.
 13. The computer program product of claim 8 wherein the LUN is included within a data array.
 14. The computer program product of claim 8 wherein one or more of the first host and the second host are application servers.
 15. A computing system including at least one processor and at least one memory architecture coupled with the at least one processor, wherein the computing system is configured to perform operations comprising: receiving a first write request from a first host concerning a logical unit number (“LUN”); assigning exclusive control of the LUN to the first host; performing a write operation on the LUN in response to the first write request; receiving a second write request from a second host concerning the LUN; and reassigning a second portion of the LUN that was exclusively controlled by the first host so that the second portion of the LUN is exclusively controlled by the second host.
 16. The computing system of claim 15 further configured to perform operations comprising: performing a write operation on the second portion of the LUN in response to the second write request.
 17. The computing system of claim 15 further configured to perform operations comprising: receiving a third write request from a third host concerning the LUN; reassigning a third portion of the LUN that was exclusively controlled by the first host so that the third portion of the LUN is exclusively controlled by the third host; and performing a write operation on the third portion of the LUN in response to the third write request.
 18. The computing system of claim 15 further configured to perform operations comprising: receiving a read request from the second host concerning the LUN; reassigning a fourth portion of the LUN that was exclusively controlled by the first host so that the fourth portion of the LUN is jointly controlled by the first host and the second host; and performing a read operation on the fourth portion of the LUN in response to the read request.
 19. The computing system of claim 15 wherein assigning exclusive control of the LUN to the first host includes: assigning exclusive control of the LUN in its entirety to the first host.
 20. The computing system of claim 15 wherein the LUN is included within a data array.
 21. The computing system of claim 15 wherein one or more of the first host and the second host are application servers. 